As is well-known in the art, in large aircraft with heavy wing mounted engines the aerodynamic forces on the outboard engines cause a significant amount of lateral and vertical movement of the outboard engines. This movement of the engines causes considerable undesirable flutter of the wing strut and the wing itself. In order to detune the frequency of the wing, strut and engine combination and to reduce the undesirable loads on the wing, such aircraft have generally been provided with a spring beam between each outboard wing strut and the wing to which it is attached. The spring beam reduces the natural frequency of the engine and the strut without causing unacceptable reduction in the strength of the strut.
The spring beams have been quite successful in protecting the wing structure, but they have also created new problems. One such problem is movement of the strut trailing edge fairing access doors. The bottom portions of these doors are located to maintain them in a closed position, and the top portions of the doors are hinged onto a skirt beam that is rigidly attached to the wing. Therefore, movement of the strut and engine creates a load on the latch mechanisms and hinge mechanisms of the fairing access doors. These loads can lead to failure of the latches, the hinges, or the doors themselves. Failure of the latches could cause the doors to fly open when the aircraft is in flight and thereby endanger the safety of the aircraft. If the latches are strengthened, the load on the hinges is that much greater and it becomes necessary to provide some means to enable the hinges to carry the load and prevent failure of the hinge structure or the access doors themselves.
In the aircraft environment, there are a number of problems associated with the need to strengthen any structure. These problems include a very limited amount of space and a need for minimizing the overall weight of the structure. In addition, if springs are involved, undesirable characteristics such as rebound and relatively low frequency must be avoided. In the particular case of the hinge load discussed above, it is also necessary to carry a very large load with a quite small deflection of the structure experiencing the load.
The following United States patents disclose spring devices for controlling motion of airfoils in aircraft:
U.S. Pat. No. Re. 18,181, granted Sept. 8, 1931, to W. Stelzer;
U.S. Pat. No. 1,885,571, granted Nov. 1, 1932, to B. F. Wilson;
U.S. Pat. No. 1,945,254, granted Jan. 30, 1934, to C. C. Bittner;
U.S. Pat. No. 1,989,291, granted Jan. 29, 1935, to R. H. Prewitt;
U.S. Pat. No. 2,066,649, granted Jan. 5, 1937, to R. C. Sabins;
U.S. Pat. No. 2,073,350, granted Mar. 9, 1937, to R. R. Osborn;
U.S. Pat. No. 2,182,366, granted Dec. 5, 1939, to J. D. Van Vliet;
U.S. Pat. No. 2,584,666, granted Feb. 4, 1952, to G. E. Bockrath; and
U.S. Pat. No. 2,757,886, granted Aug. 7, 1956, to R. E. Correa.
The Wilson and Sabins patents disclose devices for elastically mounting and controlling the movement of wings. Each of these two patents discloses a device in which a piston or plunger is biased into a center position by a pair of coil springs positioned on either side of the piston. In each case, the spring device is placed between the wing and the fuselage of the aircraft.
The following United States patents disclose apparatus in which Belleville springs or similar devices are used to control movement and/or a load:
U.S. Pat. No. 1,884,981, granted Oct. 25, 1932, to F. Otto;
U.S. Pat. No. 2,499,131, granted Feb. 28, 1950, to H. J. Coles;
U.S. Pat. No. 2,795,967, granted June 18, 1957, to L. J. Wahl;
U.S. Pat. No. 3,032,805, granted May 8, 1962, to J. A. Skupas et al;
U.S. Pat. No. 3,050,346, granted Aug. 21, 1962, to F. E. Simpson et al;
U.S. Pat. No. 3,128,071, granted Apr. 7, 1964, to A. G. Frazer-Nash;
U.S. Pat. No. 3,247,975, granted Apr. 26, 1966, to D. E. Holt et al;
U.S. Pat. No. 3,292,917, granted Dec. 20, 1966, to P. C. Sherburne;
U.S. Pat. No. 3,498,488, granted Mar. 3, 1970, to A. J. Wildey et al;
U.S. Pat. No. 3,561,747, granted Feb. 9, 1971, to A. F. Donnelly;
U.S. Pat. No. 3,649,092, granted Mar. 14, 1972, to H. R. Coleman;
U.S. Pat. No. 4,033,644, granted July 5, 1977, to J. Reneerkens; and
U.S. Pat. No. 4,073,697, granted Feb. 14, 1978, to M. Protzl.
Widley et al disclose a log skidder in which pivotal movement of a rear section with respect to a center section in either direction is resisted by a single stack of Belleville springs. The springs are confined in a cylindrical housing that is pivotally mounted on each of said sections.
The above patents and the prior art that is discussed and/or cited therein should be studied for the purpose of putting the present invention into proper perspective relative to the prior art.